1. Field of the Invention
The present invention relates to an electro-photographic apparatus, and more particularly, to a method and apparatus for development using a dry two-component developer.
2. Description of the Related Art
Conventionally, a magnetic brush development method using a two-component developer consisting of magnetic carriers and toners has been employed in an electro-photographic apparatus. A development apparatus using the method normally has a magnet roller having a magnetic body including a plurality of magnetic poles and a development sleeve which is a rotatably supported cylindrical developer supporter. The development apparatus develops by holding magnetic carriers having toners on a surface of the development sleeve and carrying them to a development area. On the other hand, a one-component development method in which development is performed by using only magnetic toners or non-magnetic toners without magnetic carriers has also been employed. The one-component development method is similar to the two-component development method in respect to development by holding toners on a surface of a development sleeve and carrying them to a development area, but different from it with respect to detailed structures and a means of charging toners, etc.
In such a development apparatus, it has been proposed to improve image quality by improving of toner carrying performance by increasing surface roughness of a development sleeve using a one-component development method as described in Japanese Examined Application Publication No. 64-12386. A method to improve performance of carrying toners by increasing surface roughness of a development sleeve using a two-component development method has also been proposed as described in Japanese Laid-Open Patent Application No. 5-19632.
However, the methods described above presuppose non-contact development and that the quantity of developer on a developer supporter is controlled to be constant by using a developer quantity controller in the form of a bar. A non-contact development method using a developer quantity controller which is made from materials having rigidity or rigidity and magnetic properties have problems in providing enough developer on a developer supporter. Especially, size of carrier particles needs to be smaller to meet recent requirement for high image quality and downsizing. However, when size of carrier particles is made smaller, fluidity of the particles tends to be lower, so that the above mentioned method has problems in carrying developer to a development area uniformly when such a developer is used.
Furthermore, in most recent copying machines, a photo conductor and a development apparatus are combined and they can be easily exchanged, providing for labor savings related to maintenance by a service person. In such a system, since cost is higher if an exchanging cycle is short, a developer having a long service life and a latent image supporter having a service life comparable to the one of the developer, which is referred to below as a photo conductor, are required. However, when the two-component contact development method is employed, a photo conductor is always rubbed with developer, and, thus, it is easy for the photo conductor to become worn and difficult to have a long servicelife. Furthermore, density of a developer on a development area is required to be high to meet the demand for high image quality. However, if density of a developer on a development area is high, wear of the photo conductor is accelerated. In order to prevent wear of the photo conductor, prevention of wear by decreasing printing resistance has been attempted by adding a filler to the outermost layer of a photo conductor. Ozone generating from a charger and low resistance materials secondarily produced from nitrogen oxides fall on an outermost layer of a photo conductor and adhere to a surface of the layer. When a photo conductor in which a filler is not added to the outermost layer is used, abrasion of the outermost layer of a photo conductor is reduced and resistance of a surface of a photo conductor is reduced by adhesion of the low resistant materials, so that abnormal images having decrease in resolution or blur are not formed. The problem originates when wearing rate of the outermost layer is faster than the deposition rate of the low resistance materials. However, the abrasion loss of a photo conductor defines the service life of the photo conductor. On the other hand, when a layer having high wear resistance is laid on the outermost layer of a photo conductor as in the subject application, abrasion loss decreases and the service life of a photo conductor is not controlled by the wear resistance. However the deposition rate of the low resistance materials produced from ozone and nitrogen oxides, etc., described above overcomes the rate of wear resulting in deposition (adhesion) of the low resistance materials to the surface of the photo conductor. Consequently, side effects such as decrease in resolution and blur in an image resulting from decrease of resistance on a surface of a photo conductor are generated, therefore a new problem of the side effects controlling the service life of an image formation apparatus occurs.
When a layer including a filler is laid on the outermost layer of the above mentioned photo conductor, the wear resistance is improved, but side effects may occur. When a conductive filler is employed as a filler, resistance on a surface of a photo conductor is reduced, and decrease in resolution and blur in an image may occur due to a reason other than the above mentioned phenomenon. Especially, the phenomenon is significant when a photosensitive layer is made from an organic material. Therefore, it is necessary to employ a high resistance filler in an organic photo conductor. In this case, since the filler does not have charge transfer efficiency, when the photo conductor is repeatedly used in an electro-photographic apparatus, residual potential is elevated or electric potential of exposed areas is elevated in negative or positive development, so that there is produced a defect of decrease in image density.
Thus, as wear resistance of a photo conductor is improved and abrasion loss does not define the service life of a photo conductor, an electrostatic service life of the photo conductor defines the service life of the photo conductor. Specifically, point defects (stains and black points, etc.) on image background (white background), which are not in an original image, occur due to decreasing electrostatic property of a photo conductor (especially, local leak of electric potential). The defects may be taken for points in a drawing or period and comma, etc., in a draft in English so that the defects are crucial in an image.
The present invention is achieved in the situation as described above. It is a general object of the present invention to provide an image formation apparatus preventing deposition of low resistance materials produced from ozone and nitrogen oxides on a surface layer of an improved wear-resistant photo conductor by providing a developer with moderate strength to the photo conductor and thereby prevent the generation of an abnormal image having blur and decrease in resolution, which is peculiar to a high wear resistant photo conductor.
A more specific object of the present invention is to provide an image formation apparatus preventing elevation of residual potential caused by repeated use of a photo conductor including a filler in an outermost layer and preventing decrease of image density in negative or positive development.
A further specific object of the present invention is to provide an image formation apparatus preventing a reduction of electrostatic properties caused by repeated use of a photo conductor and preventing point defects (stains on image background) in negative or positive development.
The inventors actively investigated the relation among developer carrying properties, diameters of developer particles and surface roughness Rz of a development sleeve in order to solve the above mentioned problems. As a result, the inventors found that when a developer having the particle diameters within a particular range is used, the developer can be uniformly provided on a developer supporter by adjusting the relation between a development gap and a doctor gap to within a particular range, a surface of a photo conductor can be always maintained in usable condition by the developer, and there is no problem about the service life of the photo conductor.
That is, the solution of the above problem is achieved by the present inventions; (1) an image formation apparatus developing an electrostatic latent image with a two-component developer consisting of magnetic carriers and toners by using a development apparatus and a latent image supporter including a filler in an outermost layer thereof, the development apparatus having a developer supporter, which has an internally fixed magnetic body and rotates while supporting a developer on a surface thereof, and a developer quantity controller controlling a quantity of the developer which is supported by the developer supporter facing the magnetic body by controlling a height of magnetic brushes and consisting of materials having rigidity or rigidity and magnetic properties, characterized in that a ratio (Gp/Gd) of a development gap to a doctor gap between the developer supporter and a controller is from 0.7 to 1.0, and a weight-averaged particle diameter of a developer carrier is from 20 to 60 xcexcm; (2) the image formation apparatus described in item (1) characterized in that surface roughness Rz of a development sleeve is from 10 to 30 xcexcm; (3) the image formation apparatus described in the item (1) and (2) is characterized in that a surface of the development sleeve is processed by sand blasting; (4) the image formation apparatus described in any one of the items (1) to (3) is characterized in that a ratio (D/Rz) of the weight-averaged particle diameter (D) of the developer carrier to surface roughness (Rz) of the development sleeve satisfies a relation 2 less than D/Rz  less than 3; (5) the image formation apparatus described in items 1 to 4 is characterized in that the filler included in the outermost layer of the latent image supporter is formed by a metal oxide; (6) the image formation apparatus described in items 1 to 5 is characterized in that the outermost layer of the latent image supporter includes a charge transfer material; (7) the image formation apparatus described in item 6 is characterized in that the charge transfer material is a polymer having electron-donating groups; (8) the image formation apparatus described in items 1 to 7 is characterized in that the outermost layer of the latent image supporter includes an organic compound of which acid value is from 10 to 40 (mgKOH/g); (9) the image formation apparatus described in items 1 to 8 is characterized in that a charge generating material included in the latent image supporter is a titanylphthalocyanine having at least a maximum diffraction peak at 27.2xc2x0 as diffraction peak at Bragg angle 2xcex8 (+0.2xc2x0) for characteristic X-ray of CuKxcex1; (10) the image formation apparatus described in items 1 to 8 is characterized in that the charge generating material included in the latent image supporter is an azo pigment represented by the following structural formula (A): 
wherein Cp1 and Cp2 are coupler residues, which are identical or different from each other; wherein R201 and R202 are respectively selected from a group consisting of hydrogen atom, halogen atom, alkyl groups containing 1 to 4 carbon atoms, alkoxy groups containing 1 to 4 carbon atoms, and cyano group and are identical or different from each other; wherein Cp1 and Cp2 are represented by the following structural formula (B) 
wherein R203 is selected from a group consisting of hydrogen atom, alkyl groups such as methyl group and ethyl group, and aryl groups such as phenyl group; wherein R204, R205, R206, R207, and R208 are respectively selected from a group consisting of hydrogen atom, nitro group, cyano group, halogen atom such as fluorine, chlorine, bromine, and iodine, trifluoromethyl group, alkyl groups such as methyl group and ethyl group, alkoxy groups such as methoxy group and ethoxy group, dialkylamino group, and hydroxyl group;
wherein Z represents an atom group required for forming a substituted or non-substituted aromatic carbon ring or a substituted or non-substituted aromatic heterocyclic ring;
(11) the electro-photographic apparatus described in items 1 to 10 is characterized in that a surface of a conductive supporter of the latent image supporter is anodized; (12) the electro-photographic apparatus described in items 1 to 11 is characterized in that in the electro-photographic apparatus, a charger contacts or is closely arranged to the latent image supporter; (13) the electro-photographic apparatus described in item 12 is characterized in that the size of air gap between the charger and the latent image supporter is equal to or less than 200 xcexcm; (14) the electro-photographic apparatus described in items 12 and 13 is characterized in that in the electro-photographic apparatus, an alternating current component is superposed on a direct current component in the charger to provide a charge to the latent image supporter; (15) the electro-photographic apparatus described in items 1 to 14 is characterized in that zinc stearate is applied on the latent image supporter; (16) the electro-photographic apparatus described in item 15 is characterized in that in the electro-photographic apparatus, zinc stearate powder is included in the toner provided to a development area.
The development method according to the present invention is a two-component contact development method carried out by using a development apparatus having a developer supporter, which has an internally fixed magnetic body and rotates while supporting a developer on a surface thereof, and a developer quantity controller controlling a quantity of the developer which is supported by the developer supporter facing the magnetic body and consisting of materials having rigidity or rigidity and magnetic properties.
At first, the development apparatus according to the present invention will be illustrated. FIG. 1 shows a cross section of a development apparatus according to the present invention. In FIG. 1, it is shown that the reference numeral 1 is a photo conductor drum, 2 is a development sleeve housing, 3a is toner, 4 is a development sleeve, 5 is a magnet roller, 6 is a controller, 7 is a sleeve in front of a doctor, 7a is a diaphragm, 8 is a toner hopper, 8a is an aperture for supplying toners, 9 is a provision roller, 12 is a development area, A is a developer providing room, Gp is a development gap, and Gd is a doctor gap.
Herein, the photo conductor drum rotates in the direction indicated by the arrow, has the outermost layer including a filler on the surface of the photo conductor and forms an electrostatic latent image on the surface by a charger and an exposure device not shown in FIG. 1. The magnet roller 5 is fixed in the development sleeve being the developer supporter, has a plurality of (N), (S) magnet poles on the surface of the roller, supports the developer with the development sleeve, and carries the developer, in which the development sleeve 4 rotates in the same direction as the rotational direction of the photo conductor against the fixed magnet roller. The magnetic poles (N), (S) of the magnet roller 5 are magnetized to an appropriate magnetic flux density so that magnetic brushes consisting of the developer are formed by the magnetic force. The controller 6 controls the height and the quantity of the magnetic brushes. The distance between the controller and the development sleeve is referred to as doctor gap (Gd).
While the toner 3 provided into the apparatus is sufficiently stirred and mixed with the carriers by the provision roller 9 rotating in the direction indicated by the arrow and frictional electrification is carried out, the toner is carried to the development sleeve housing 2, and magnetic brushes of which the height and the quantity are controlled by the controller 6 are formed on the development sleeve 4. When the distance between the development sleeve 4 and the surface of the photo conductor drum 1, or development gap (Gp) is set to the predetermined distance (for example, 0.7 mm) and a electrostatic latent image is developed on the photo conductor drum, the magnetic brushes formed on the surface of the development sleeve 4 are vibrating due to a change of the magnetic flux density and moved with the development sleeve 4 while the development sleeve 4 rotates, and the magnetic brushes pass smoothly through a gap in the development area and a latent image is developed by the toner. In this case, a bias voltage may be preferably applied between the development sleeve 4 and the substrate of the photo conductor drum 1 in order to carry out the development.
The development method according to the present invention satisfies the condition that in the two-component development device shown in FIG. 1, the magnetic carriers of which the weight-averaged particle diameter is from 20 to 60 xcexcm are utilized and a ratio (Gp/Gd) of the development gap (Gp) to the doctor gap (Gd) is from 0.7 to 1.0. If Gp/Gd is less than 0.7, adhesion of carriers is easily generated since a pool of the developer occurs in the development gap. On the other hand, if it is larger than 1.0, the developer is weakly applied to the photo conductor resulting in elimination of a cleaning effect. If the diameter of the carrier particle is less than 20 xcexcm, it is not preferable since carrier adhesion easily occurs. If it is larger than 60 xcexcm, although there is no notable trouble, it is not preferable due to a demand for high image quality. Also, surface roughness (Rz) of the surface of the development sleeve satisfies the condition of from 10 to 30 xcexcm. Satisfaying the condition results in not only generating more cleaning effect but also stabilizing the providing of the developer, and is effective in improving image quality.
The surface roughness Rz means ten points-averaged roughness, and for example, it may be measured by Surfcoder SE-30H produced by Kosaka Laboratory. The ten points-averaged roughness reflects the depth of fine irregularities of a solid surface. Also, a material used in a development sleeve may be one used in a normal development apparatus, non-magnetic materials such as stainless steel, aluminum, and ceramics, and a coated development sleeve may be used but is not required. The form of the development sleeve is also not particularly limited.
In the present invention, in order to adjust the surface roughness Rz of the development sleeve to within the above mentioned range, although, for example, sand blasting, groove processing, grinding, sand paper, and index saver processing may be used, it is preferable to use sand blasting in respect to the following points. That is, since sand blasting is not only easy to operate and efficient to process but also can be used for a random surface processing (coarsening), frictional resistance between the toner and the development sleeve is considered to be improved equally in all directions.
It is effective for the ratio (D/Rz) of a weight-averaged particle diameter of a carrier (D) to surface roughness (Rz) of the development sleeve to satisfy a relation 2xe2x89xa6D/Rzxe2x89xa63, in order to improve the effect of the present invention. Even if the ratio does not satisfy the relation, there is no problem with respect to the cleaning effect of the photo conductor. However, if the ratio D/Rz is less than 2, stress applied on the carrier become larger and peeling off of carrier coating resin or carrier pollution with the toners easily occurs. On the other hand, if the ratio D/Rz is larger than 3, toner density becomes too high or a defect on carrying performance is generated a little when Q/M become too large.